1. Field of the Invention
The present invention relates to miniature zoom lens systems and, more particularly, to a miniature zoom lens system which is applicable to the image capture module of a handheld communication device and which uses only three lens groups, which consist of four lenses in total, to provide a high zoom ratio while still having a small volume and good optical quality.
2. Description of the Prior Art
Recently, picture-taking and video recording functions have gradually become indispensable features of handheld communication devices such as cell phones, personal digital assistants, and notebook computers. As the image capture module of a handheld communication device must be compact and energy-saving, it is imperative to miniaturize the optical lens systems of such image capture modules and ensure that the lens systems deliver good optical performance.
In a miniature optical lens system having a focusing or zooming function, it is typically required that at least two lens groups and an electromagnetic driving device for driving the lens groups be arranged in a tiny space not larger than 15 mm3. As a result, the number, size, and weight of the lenses used are all minimized. Presently, optical lens systems with a three-lens-group four-lens structure have been developed, as disclosed by U.S. Pat. No. 7,019,912 and U.S. Pat. No. 7,312,930. However, the known miniature optical lens systems still have bottlenecks and blind spots in design. More specifically, existing miniature optical lens systems either achieve compactness at the expense of zoom ratio or optical quality or vice versa. In U.S. Pat. No. 7,019,912, for example, the zoom ratio reaches no higher than approximately 2×, which does not meet consumers' general expectation of a zoom lens system. In U.S. Pat. No. 7,312,930, although the zoom ratio approaches 3×, the overall length of the lens system comes to 15.86 mm in an embodiment with a zoom ratio of 2.48×, and 17.91 mm in an embodiment with a zoom ratio of 2.93×. The excessively great overall length of the lens system directly increases the overall volume of the lens system and therefore needs to be reduced. In addition, the lens systems of the afore-cited patents also leave room for improvement in terms of optical quality.